This invention relates to a phosphor and a method for producing the same, and more particularly to a phosphor mainly made of a solid solution which is formed of gallium nitride and indium nitride and doped with a doping substance, resulting in emitting light due to excitation by electrons, and a method for producing such a phosphor.
Japanese Patent Application Laid-Open Publication No. 41686/1976 discloses a phosphor of which a matrix is made by subjecting Ga.sub.2 O.sub.3 to nitriding in an ammonia atmosphere and doped with Cd. The phosphor disclosed is not applied to luminescence due to excitation by electrons and the Japanese publication described above is silent concerning luminescence due to excitation by electrons. A phosphor GaN which is doped with Zn or Mg acting as a dopant is known in the field of an LED, however, it is not a phosphor excited by electrons.
Nitriding of Ga.sub.2 O.sub.3 in a nitrogen atmosphere causes Ga.sub.2 O.sub.3 to be nitrided from a surface thereof. However, exposure of the nitrided Ga.sub.2 O.sub.3 to a high temperature causes a surface thereof to be oxidized again. More specifically, gallium nitride is apt to cause nitrogen to be removed therefrom and be oxidized by oxygen. Thus, use of Ga.sub.2 O.sub.3 as a starting material for the phosphor renders complete nitriding of Ga.sub.2 O.sub.3 highly difficult, so that gallium nitride obtained fails to exhibit satisfactory quality because oxygen remaining in the nitride adversely affects luminescence of the phosphor. Also, supposing that gallium nitride were applied to an element excited by electrons, a powder of gallium nitride acting as a phosphor would be deposited on a substrate and then subject to calcination in an ambient atmosphere. Thus, the phosphor would be subject to various heat treatments during manufacturing of the element, resulting in a surface of the phosphor being possibly deteriorated.
Also, doping of gallium nitride with a doping material by a normal thermally-equilibrated reaction requires to increase a reaction temperature to a level as high as 1100.degree. C. or more. Unfortunately, gallium nitride starts sublimation at a temperature of about 800.degree. C. Thus, production of the gallium nitride phosphor by the normal thermally-equilibrated reaction requires to set troublesome conditions such as heating under an increased pressure, so that the production is rendered highly difficult or substantially impossible.